Rubber mixtures

ABSTRACT

LIGHT-COLORED, TECHNICALLY VALUABLE VULCANISATES ARE OBTAINED ACCORDING TO THE INVENTION WHEN NATURAL OR SYNTHETIC RUBBER IS VULCANISED IN THE PRESENCE OF INSOLUBLE AND INFUSIBLE, FINELY DISPERSED AMINOPLASTS HAVING AN INNER SURFACE OF MORE THAN 10 SQUARE METERS PER GRAM AND AN AVERAGE PARTICLE SIZE SMALLER THAN 5U.

United States Patent G s. c1. 2603 4 Claims ABSTRACT OF THE DISCLOSURE Light-colored, technically valuable vulcanisates are obtained according to the invention when natural or synthetic rubber is vulcanised in the presence of insoluble and infusible, finely dispersed aminoplasts havingan inner surface-of more than 10 square meters per gram and an average particle size smaller than 5 This application is a continuation-in-part application of our copending application Ser. No. 389,197, filed Aug. 12, 1964, now abandoned.

Vulcanisates from natural rubber or synthetic elastomers are manufactured by dispersing in the crude mixtures finely divided solid substances that interact with the molecules of the polymer and thereby determine to a large extent the physical properties of the finished vulcanisate. 'Since certain of these insoluble and infusiblesolid substances .improve the technical properties of the final products, they are also referred to as active or reinforcing fillers.

The rubber industry makes preferred use of carbon black as filler and uses it on a very large scale. However,

apart from its good reinforcing properties carbon black has thegreat disadvantage that it is black so that it is excluded from many uses. In recent times a number of further, predominantly inorganic, solid substances have been adopted, generally called white fillers for short, such as silicic acid, silica gel, aluminum silicates, calcium silicates, alumina gel, calcium carbonate, China clay, chalk, ground mica, illite, gypsum, zinc oxide and magnesium oxide. These substances have a relatively high specific gravity which is undesirable for some structural purposes. In addition, many of them produce only a minor reinforcing effect and even the most active in this group of white fillers do not reach the reinforcing action produced by good types of carbon black. Now there has been found a process for making a new type of finely dispersed, insoluble and infusible aminoplast fillers and vehicles having a specific surface area greater than 10 square meters per gram. For example a solid phase is formed from an aqueous solution of melamine and formaldehyde at a molecular ratio of from 1:15 to 1:6 at a temperature from 20 to 100 C. and at a pH value from 6 to 0, this phase is then freed at least largely from inorganic salts, then freed from water at a temperature between 30 and 160 C. and comminuted to an average particle size smaller than 5 In the conventional processes for the manufacture of condensation'pro'ducts from melamine and formaldehyde it is usual to ensure. by suitable measures-for example by discontinuing. the resinification reaction before term or by reacting the components within a pH range from 6 to .10that products are obtained which are soluble or insoluble, or at least still fusible, so that they can be cured in a follow-up stage. In contradistinction thereto the insoluble, infusible'aminoplast fillers are fully crosslinked 3,553,115 Patented Jan. 5, 1971 resins that can no longer be shaped and at the same time cured.

Surprisingly, it has been found that light-colored, technically voluable vulcanisates are obtained according to the invention when natural or synthetic rubber is vulcanised in the presence of insoluble and infusible, finely dispersed aminoplasts having an inner surface of more than 10 square meters per gram and an average particle size smaller than 5,11.

The present invention does not include the preparation of the finely divided aminoplasts.

In the following description and in the patent claims the term amino-aldehyde resin or aminoplast respectively has the well-accepted meaning in the art. In particular, it comprises the condensation products of aldehydes, especially formaldehyde, optionally in conjunction with other aldehydes such as acetaldehyde or acrolein, with aminoplast formers such as urea, thiourea, guanidine, dicyandiamide, acrylamide, aniline and aminotriazines, especially melamine, and ethylene urea.

Apart from melamine the foremost amino-triazine components are guanamines such as formoguanamine, acetoguanamine, lauroguanamine, A tetrahydrobenzoguanamine, hexahydrobenzoguanamine and benzoguanamine.

Radicals containing hydroxyl groups, present in the amino-aldehyde resins, such as methyol groups, may also be wholly or partially etherified with methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, allyl alcohol, methallyl alcohol or Z-buten-l-ol.

The aminoplast resins to be used according to the invention may also contain modifying additives or they may have been sulfurated. Such additives are phenol,

'cresols, Xylenols, especially in the form of precondensates based on formaldehyde and phenol, cresol or xylenol, and the methylol compounds or novolaks of a higher degree of condensation may be added at any desired condensation stage. Further suitable additives are aniline and alkylanilines and their formaldehyde resins, carboxylic acid amides such as acetamide, hexamethylenetetramine, ethyleneimino polymers and natural resins, such as colophony or copal resin. The sulfurization is generally performed by adding sulfur or sulfur donors, such as hydrogen sulfide, di-sulfur dichloride, ammonium sulfide or polysulfides. The sulfur content thus achieved may have a favourable influence on the vulcanisation and improves the formation of main valencies between filler and rubber. By incorporating 'mercaptans at the methylol groups of the nitrogenous resin component it is possible to achieve at the same time an acceleration of the vulcanisation, for example by the known addition reaction of mercaptobenzthiazole with the methylolmelamines.

In a preferred variant of the present process there are used resins which are cured or condensed respectively in the presence of surface-active substances of the nonionic or ionic kind, for example nonionic polyalkylene ethers or natural products, such as tragacanth, gum arabic, anionic fatty alcohol sulfonates, alkylaryl sulfonates, isomerized abietic acid, salts of sulfonsuccinic acid esters, or cationic quaternary ammonium bases. The latter are of advantage, for example, when a particularly good compatibility with the generally negatively charged latex particles is aimed at. v

The cured, finely dispersed aminoplasts can be incorporated in the'rubber on a roller mill or they may be admixed with the latex.

The amount of aminoplast powder to be added may vary 1% to referred to the weight of the mixture as a whole; a preferred proportion is 5% to 35%. A

The term rubber asused in the present specification and in the patent claims has the wide meaning generally used in the rubber industry which includes both the olefin elastomersand the rubber-like polycondensates and polyadducts. Apart from natural rubber and its derivatives, such as chlorinated rubber, cyclo rubber and cationically treated latex there may be mentioned above all the polymers and copolymers of butadiene, isoprene and chloroprene, such as normal, atactic polybutadiene, syndiotactic and isotactic 1,2-polybutadiene, cis-l,4-polybutadiene, trans-1,4-polybutadiene, poly-2,3-dimethylbutadiene, cis-1,4-polyisoprene, butyl rubber, chlorinated butyl rubber, copolymers from butadiene and styrene or methylstyrene, acryonitrile, 2 methyl-S-vinylpyridine, vinylpyridine, methacrylate, acrylates, dialkylacrylic acid amides and nuclear-halogenated styrenes. To this class belong also chlorinated and sulfochlorinated polyethylene, copolymers of vinylchloride with ethylene, vinylidenefluororide copolymers with trifluoroethylene or hexafluoropropylene, ethylene-butene-l and ethylene-propylene copolymers such as ethylene-propylene terpolymers with dicyclopentadiene, 1,4-hexadiene, Z-methylene-norbornadiene and the like as the tertiary component; silicone rubber, fluorinated silicone rubbers, urethane rubbers, tetrafluoroethylene-trifluoronitrosomethane copolymers, thiocol rubber and polyphosphorus nitrile chloride and its derivatives in which the chlorine atoms are replaced by alkyl, aryl, alkoxy or aryloxy groups, as Well as their mixtures or copolymers.

Apart from the additives of finely dispersed aminoplast filler according to this invention the mixtures to be vulcanised may contain any of the usual rubber additives and compounding substances, that is to say that, apart from vulcanising agents including actinic and corpuscular irradiation, there may be added accelerators, activators,

The rubber mixes used in, the example, were prepared with the following aminoplasts:

Manufacture of insoluble aminoplasts having a large inner surface.

AMINOPLAST A A mixture of 126 parts of melamine and 200 parts of a 30% aqueous solution of 'formaldehyde ,(which. had first been adjusted to pH=8 .5 with 0.9'part by volume of N-sodium hydroxide solution) is heated to 85 C.,'with the melamine passing into solution. This solution-is diluted by tipping in a mixture, heated to 94' C., off 84 parts of a 6% aqueous tragacanth solution and 4000 parts of water. Within 3 to 10 minutes 100 parts by volume of 10% sulfuric acid are vigorously stirredin whereupon a White precipitate forms. The whole is allowed to cool to C. and the mixture, which'has a pH of 4.45, is then filtered. The filter radicalis washed copiously with water, until sulfate ions can no longer be'detec ted in the filtrate. The moist filter cake is subjected to' a'zeotropic distillation until no more water separates, whereupon the bulk of benzene is filtered off. The white, pulverulent resin is freed from benzene in a drying cabinet at C until'its weight remains constant and then ground for 4 hours in a porcelain ball mill, to yield 151' parts -of a white powder which passes through a sieve having an inner mash size of 0.1 mm., has a bulk weight of 11.5 g. per ml. and a specific surface area of 76 square meters pergram p 3 The following aminoplasts are manufactured in an identical manner;

1 Instead of 100, 20 parts by volume of sulfuric acid are used. 2 The formaldehyde solution was adjusted to pH 6.0 with sodium hydroxide solution. 1 3 In this case the amount of ammonium disulfide used corresponds to 0.3 gram atom of sulfur.

decelerators, antioxidants and heat stabilizers, glues and other white fillers. Furthermore, there may be added dyestuffs and pigment colors. The mixtures may also contain inorganic oxides or thermoplastic resins such as polyvinylchloride and epoxy resins as compounding substances.

By virtue of their light colors the vulcanisable mixtures of the invention may be used with special advantage wherever the black color of carbon black is unacceptable, for example in the manufacture of white or light-colored rubber articles in industry and'the home, such as rubber goods for the household, sundries, toys, industrial rubber goods and sidewalls of automobile tires.

By comparative tests it can be shown that the use according to-the invention of a finely dispersed aminoplast as filler leads to light-colored vulcanisable rubber having mechanical strength properties that are certainly equal to those obtained .with good types of carbon black.

In addition, rubber vulcanisates containing aminoplast' resins, for example melamine-formaldehyde resins, according. to. the invention,-in the same proportions as a comparablevulcanisate containing an inorganic white filler, have a lower specific gravity.

@Unless otherwise indicated, parts and percentages in the following examples are by weight. The relationship between .partsby volume and parts by weight isthe same as that between-the milliliter and thegram.

' AMINOPLAST F.

A mixture of 4 parts of a 50% aqueous solution of monobasic monoethanolamine phosphate and 400 parts of 30% aqueous formaldehyde solution is adjusted with 13.5 parts by volume of N-sodium hydroxide solution to pH 6.00. The mixture is heated with 126 parts of melamine to 60 C. After 15 minutes a clear, colorless solution has formed. Tomaintain the temperature at 60 C.,- moderate, cooling is required. 30 minutes after addition of the melamine, the melamine-formaldehyde precondensate has a pH value of 6.71 at 60 C. The batch is cooled to 20C.,;. whereupon the solution has a pH of 6.85, diluted with a solution of, 18.2 parts of a 25% aqueous solution of a; nonionic dispersant marketed under the registered trademark Emulphor 0 (obtained by condensing a higher fatty alcohol with ethylene oxide) and with 108 parts of a 50% aqueous solution of monobasic monoethanolamine phosphate in 262 parts of water. The mixture is adjusted with 127 parts by volume of dilute hydrochloric acid (1- part by volume of concentrated hydrochloric" acid to -:-1l-' part of water) to a pH'of 2.70, heated for:6 hoursat-45 9.; (3.; theresulting, firm, white gel is thencomminuted with; a stirrer with 1100 parts of waterand 138 parts by volume: of concentrated ammonia until it'forms a :white; paste? having a pH value of 8.0. The whole-is. kept for l0ahours;

at room temperature, filtered and washed with water until chlorine ions can no longer be detected in the filtrate. The moist filter cake is subjected to azeotropic distillation with benzene until water no longer separates, whereupon the bulk of the benzene is filtered off. The white, pulverulent heated for 6 hours at 45 C. and the aminoplast formed is isolated as has been described for aminoplast F. Yield: 202 parts of a white powder which has a bulk weight of 10 g./100 ml. and a specific surface area of 174 m. gram.

resin is freed from benzene in a drying cabinet at 80 C. AMTNOPLAST R until its weight remains constant, to yield 191 parts of a white powder which is ground for 4 hours in a porcelain 60 parts of urea are dissolved at room temperature in ball mill. The resulting ground material passes through 200 parts of an aqueous 30% formaldehyde solution, then a sieve having an inner mesh size of 0.1 mm. It has a bulk diluted with 31.4 parts of a 25% aqueous solution of the weight of 19 g. per 100 ml. and a specific surface area of dispersant 'Emulphor 0 (used above for manufactur- 260 mF/g. ing aminoplast F), 109.5 parts of a 50% aqueous solu- The following aminoplasts were manufactured in a .tion of monobasic monoethanolamine phosphate and 238 s'imilar'manner: parts of water, and then adjusted with 85.6 parts-- by TABLE 2 Yield per Spec. Mela- 30% aqueous mol of amide Bulk surface mine, formaldehyde components, weight, area,

mol Modifier used, mol solution, mols grams g./100 m1. mfl/g 0.97 Acrylamide, 0.03 4 207 13 120 0. 97 Ammonium disulfide 1 0.03 4 174 14 436 1 Allyl alcohol, 1.0 4 212 12 201 0.7 .Thiourea, 0.3 3.4 145 10 218 0. 97 'Monoamide from linoleic acid and diethylenetriaminefi 0.03 4 198 11 329 0. 9 Monoamide from linoleic acid and diethylenetriamine, 0 03 4 199 11 252 0. 7 Lauroguanamine, 0.3 4 209 13 60.6 0.7 Urea, 0.3 3.2 149 24 262 I In this case the amount of ammoniumdisulfide used corresponds to 0.03 gram atom of Sulfur. {Obtained by reacting 1 mol of linoleic acid with 1 mol of diethylenetnannne at 200 0., accompanied by elimination of water.

AMINOPLAST P 200 parts of 30% aqueous formaldehyde solution and 2 parts of a 50% aqueous solutionof monobasic monoethanolamine phosphate are adjustedwith 11 parts by volume of'N-sodium' hydroxide solution to pH 8.00. The whole is mixed with 126 parts of melamine and heated for l'hour at 70 C. The resulting clear solution is cooled to C. and then diluted with 2l8.6parts of a aqueous solution of the dispersant-Emulphor 0" (used above for the manufacture of aminoplast F), with 181 parts of a 50% aqueous solution of monobasic monoethanolarnine phosphate and with 590 parts of water. The batch is adjusted with 111 parts by volume'of concentrated hydrochloric acid to pH 2.22, then heated for 6 hours at 45 C. and'the aminoplast formed is isolated as described for aminoplastF, to yield 142 parts of a white powder which has a bulk weight of 10 grams per 100 ml. and aspecific surface area of 177 m. g.

AMINOPLAST Q 600 parts of aqueous formaldehyde solution and 3 parts of a 50% aqueous solution of monobasic monoethanolamine phosphate are adjusted with 14.8 parts by volume of N-sodium hydroxide solution at pH 6.5. The whole is heated with 126 parts of melamine for 30 minutes a t 50f C., and the resulting clear, colorless solution of the precondensate is: cooled to 20 C.; this solution isdiluted with 600 parts of water, 26.7 parts of an aqueous .25 solution of the dispersant Emulphor 0 (used. abovefor the manufacture of aminoplast F) and 238 parts ofan aqueous 50% solution of monobasic monoethanolamine phosphate. The batch is adjusted with 62 parts by volume ofdilute hydrochloric acid (1 part by volume of concentrated hydrochloric acid to 1 part'of water) to a pH value of 4.5. The batch is then volume of dilute hydrochloric acid (1 part by volume of concentrated hydrochloric acid to 1 part of water) at 20 C. to a pH value of 1.0. The batch is heated for 6 hours at 45 C. and the aminoplast thus formed is isolated as described for aminoplast F. Yield: 49 parts of a white powder which has a bulk weight of 11.5 g./ 100 m1. and a specific surface area of 73 mP/gram.

The rebound resilience values shown in the following examples were determined with the aid of the test gear of the Institut Fraugais du Caoutchouc (makers: Mcanique Industrielle dEnghien) whose pendulum has an energy content of 5 cm. kg. (at amplitude) and strikes from an amplitude of 90 two discs of 4.5 mm. thickness and 44.6 mm. diameter placed one on top of the other. The rebound of the pendulum is expressed in percent of the recovered energy content. In the static test to determine the hysteresis and resilience the test piece is made to French Standard Specification NFT 43-002 as a ring having an external diameter of 52.6:02 mm.,' an internal diameter of 44.6:02 mm. and 4.5 mm. thick ness. The relevant tensile stress test is performed accord ing to French Standard Specification NFT 46-002, the stress-strain diagram being plotted to a stretch of 300%. From the area of the hysteresis loop the hysteresis is computed in the known manner. Accordingto definition the resilience is -hysteresis (in percent).

EXAMPLE 1 V Vulcanising natural rubber in the presence of aminoplasts A 2-r0llmill is used for preparing a mixture from 100 parts of natural rubber, 2..parts of stearic acid, 5 parts of zinc oxide,.30 parts of one of the finely divided aminoplasts described. above, 3 parts. of diethylene-glycol, 2 parts of the plasticiser marketed by. Messrs.- Sun Oil Co. under the registered trademark Circolight Process Oil (a naphthenic petroleum fraction having .a flash point of C. and containing 19% of aromatic carbon atoms, 40% of naphthenic carbon atoms and 41% of ,Afteri'vulcanisation for 15 minutes C1, the paraffinic carbon atoms), 2.3 parts of sulfur, 0.8 part l P Q revealed the l qw goptinrnnr r PeIti i of the vulcanisation accelerator marketed by Messrs. Tensile strength-120 kg./cml Monsanto under the registered trademark Santocure Modulus at 300% elolllgatioflfllrfi (consisting of N-cyclbhexyl-Z-benzothiazolesulfenamide) Ultimate e1ngatin 3'25%' nd 0 3 art of zinc dieth 1 dithiocarbamate The 1i ht- Shore hardness a p y Tear strength-38 kg./crn. I

colored, homogeneous test pieces obtained by vulcanlsa- Rebound resi1ience 45% I I I tion at 143 C. revealed the following properties: Abrasion- 685 cu cmQ/HiR/hr. TABLE 3 Aminoplast used A B O D E F G H J K M N O P Q, R

Vulcanisation time, minutes Tensile strength, ASTM D412, kgJcm. Modulus at 300% stretch ASTM D412, kg./cm Ultimate stretch, ASTM D412, percent Shore hardness A i. 61 52 67 66 71 Tear strength, ASTM D624, test piece A, kgJcm. -121 131 ----98 Rebound resilience, percent Static test:

1st cycle:

Hysteresis, percent Resilience, percent- 10th cycle:

hysteresis, percenJ 31.5 Resilience, percent 68 5 Abrasion (French Standard Specification NFT 46- 012) cu. cm.[HP/hour 684 Exmete For comparison natural rubber, filler by a typical op- M v a I v p ti'mum recipe with Carbon m with 5111c aero' Vulcanising chloroprene rubber in the presence of an gel respectively, was vulcanised, using the following two aminoplast fluxes: The following rubber mix was prepared on a 2-roll mill: M I, M II,

p a rts garts 1 Parts Naturalrubber, smoked sheets 100 100 Neoprene. W 'T'T"' 100 Stearic acid 2 2 Steam acid 0.5 Zinc oxide 5 Maglite D0 4 Diethyleneglycol 2 Circolight Process Oil, p '3 Arninop lastL 30 Accelerator Na 22. f 2

i Vulcan 6 is the registered trademark ofacarbon black marketed by 1 Neoprene is the registered trademark of neopren Messrs Cabot rubber marketed by Messrs. 'Du Pont de Nemours.

Z Hisil 233 is the registered trademark of a silica gel marketed by 2 Ma r I ghte D 1s the registered trademark of magnesium Messrs. Columb a Southern Chemical Corp. gqgk i g iq gqzg 51 f (A d t a v k i f p I cce era or a is e regis ere ra emar o a The above mlxes were vu1CaT1 1Sed at the Optlmum mercaptoimidazoline 1 marketed by Messrs. .Du Pont de perature of 143 C. The test piecesrevealed the follow- Nemoursr p u r. e ing properties; To ensure optimum vulcanisation,the mix was vul I canised for, 50 minutes at 150 0., whereupon the/test g ulcalnisation 131mm]? minutes; 20 2%)? pieces revealed the Q l p fiifis I ens es reng g. cm. 2 Modulus at 300% elongation, kg./crn. Tenfille Strength 193 kgjcm' glltimalte glongagion, percent 632 Ultimate StICtCh230% ore ar ness I Tear strength, kg./cm 129 55 Shore hardness A80 Rebound resilience, percent 36 Tear strength50 kg./ cm.

836 Rebound resilience40% Abrasion585 cu. cm./H.P./hr.

Abrasion cu. cmJHP/hour .I-

EXAMPLE 2 g v v r EXAMPLE 1 p I I I Vulcanising styrene-butadiene rubber in the presence of Vulcanising nitrile rubberin the presenceof anaminoplast an plast The following rubber was prepared on'a 2-roll; The following mix was prepared on a 2-roll mill: 7 1 I v p 7 a Parts ButacrilBT 20s" 100 Copolymer from 76.5% of butadiene and 23.5% of Stearic acid 1 styrene 100 Zinc oxide Y 5 Stearic acid 2 Aminoplast P and L respectively u 30 Zinc oxide 5 Diethyleneglycol 7 1 2'2 AminoplastQ 30 Circolight Process Oil 1 3. Diethyleneglycol 2 Sulfur -3, Circolight- Process Oil 3 Santocure 1 31 1' Sulfur 2 Tetramethyl thiouram disulfide- 0, Santocure 1 2 Butacril ET 205" 1 5116 registered tie ,arkgut anitril ruh Zinc diethyl dithiocarbamate 0 .5 marketed by Messrs-{T511191 The resulting test pieces revealed the following properties:

We claim:

1. In a process for the manufacture of light-colored rubber vulcanizates, wherein a member selected from the class consisting of natural and synthetic rubber is vulcanized in the presence of particulate reinforcing agents, the improvement which consists in adding the reinforcing agent as an insoluble and infusible, finely dispersed amino-aldehyde resin having a specific surface area of more than 10 square meters per gram and an average particle size smaller than 5 2. In a process for the manufacture of light-colored rubber vulcanizates, wherein a member selected from the class consisting of natural and synthetic rubber is vulcanized in the presence of particulate reinforcing agents, the improvement which consists in adding the reinforcing agent as an insoluble and infusible, finely dispersed aminoaldehyde resin having a specific surface area of more than 10 square meters per gram and an average particle size smaller than 5n, said amino-aldehyde resin being selected from the group consisting of a melamineformaldehyde resin and a urea-formaldehyde resin.

3. The improvement as claimed in claim 2, wherein finely dispersed amino-aldehyde resins are used that have been rendered insoluble in the presence of a surfaceactive substance.

4. The improvement as claimed in claim 2, wherein the amount of amino-aldehyde resin filler used makes up 180% of the weight of the vulcanizate as a whole.

References Cited UNITED STATES PATENTS 3,003,990 10/1961 Umland et a1. 26038 3,238,156 3/1966 Kohrn 2602.5

FOREIGN PATENTS 723,318 2/1955 Great Britain 2603 824,252 11/1959 Great Britain 2603 518,033 11/1955 Canada 2603 OTHER REFERENCES Winspear, George: Rubber Handbook, The Vanderbilt Co., New York, N.Y., 1958, p. 338.

MURRAY TILLMAN, Primary Examiner M. J. TULLY, Assistant Examiner US. Cl. X.R. 

